In addition to classical radiography systems in which a radiographic image of a patient is recorded on radiographic hard copy film, computed radiography systems based on storage phosphor technology are nowadays commonly used.
In such a computed radiography system a cassette conveying a photo-stimulable phosphor screen is exposed to a radiation image of a body part of a patient.
All kinds of data to be associated with the image such as demographic data (patient name, gender, date of birth etc.) and data relating to the exposure such as mAs, kV etc. are entered in a workstation or are retrieved from a hospital information system or a radiology information system.
These data are then transferred onto an identification means which is coupled with the cassette. For example the data are written into an EPROM device which is provided on the cassette conveying the exposed phosphor screen or the data are transferred via radio-frequency transmission to a radio-frequency tag provided on the cassette.
The identified cassette conveying an exposed photo-stimulable phosphor screen is then fed into a read out apparatus (also referred to as a ‘digitizer’) where the identification data are read from the identification means and where the radiographic image which is stored in the phosphor screen is read out. The radiographic image is read out by scanning the exposed photo-stimulable phosphor screen with stimulating radiation and by converting the image-wise modulated light which is emitted by the screen upon stimulation into a digital signal representation of the radiographic image.
A radiographic study often comprises more than one radiographic image. For example a study of a hand comprises two or three images on different cassettes.
In such a case several cassettes each containing a photo-stimulable phosphor screen are exposed to a radiation image of the patient in different positions or to different body parts of the patient. Commonly the individual images part of a study are taken in sequence. Then the exposed cassettes are taken to the identification station where identification of the individual images is performed.
Alternatively identification of all cassettes is performed prior to exposure.
It is clear that this procedure might result in erroneous identification because different data are to be associated with exposed cassettes which contain different images but which on the outer side are indistinguishable.
It is also possible that the data which are associated with the cassette correspond with the intended circumstances, for example the intended or default settings of the X-ray source but which, due to various possible circumstances do not exactly represent the effectively applied radiation data.
Information and complaint studies have learnt that the identification procedure in radiology departments in which cassette based systems are used, is experienced as complex and error prone during every step of the workflow.
Still another problem is that there is no feed back to the operator whether the cassette intending for exposure has been properly erased and is thus free from image information before a new exposure is performed.
It is thus clear that correct association of all kinds of identification and exposure related data as well as feedback on the status of the screen within a cassette is a crucial part within the workflow of a radiology department which influences the efficiency of operations within the radiography department.
Apart from computed radiography systems digital radiography systems are gaining importance. In such a system a digital radiography detector such as a Cmos based x-ray detector is exposed to a radiation image and a digital signal representation of the image is directly generated. The signal can then be applied to a hard copy recorder, a work station or a picture archiving system (PACS). Also in this type of systems adequate and error proof association of identification and exposure data and feedback of the status of the detector (exposed, ready for exposure etc.) is required.
It is an aspect of the present invention to provide a method and apparatus that overcomes the above-mentioned problems associated with the prior art workflow.